1. Field of the Invention
The present invention relates to an electronic flashing device which uses a voltage controlled switching device such as an insulated gate bipolar transistor (IGBT) as a switching device to control light emission and extinguishment of a flashing discharge tube.
2. Related Background Art
A recently developed insulated gate bipolar transistor (hereinafter referred to as IGBT) is small in size and low in loss so that it is ideal as a light emission control switching device (hereinafter referred to as a light emission control device) of the electronic flashing device, and it has recently been used as the light emission control device of the electronic flash device. The IGBT has three terminals, a gate, a collector and an emitter and it is a voltage controlled switching device whose conduction and non-conduction between the collector and the emitter are controlled by a voltage applied between the gate and the emitter, like a FET.
In order to conduct the IGBT, a medium voltage of about 20-40 volts is applied to the gate (control terminal) assuming that the emitter is at a ground potential, and in order to non-conduct the IGBT, the gate and the emitter are kept at the same potential. Accordingly, a power supply voltage (3-12 volts in a conventional stroboscope) is too high as a drive voltage applied to the control terminal in order to turn on or off the IGBT, and a voltage of a main capacitor (usually 200-500 volts) which stores a discharging charge of the flashing discharge tube) is too high. Accordingly, it is necessary to separately provide a power supply to control the IGBT, and there is a problem in the cost and the space.
U.S. Pat. No. 4,697,906 discloses an electronic flashing device which uses a large size bipolar transistor to control a current flowing through the flashing discharge tube and a voltage doubler circuit for applying a voltage which is approximately double of a voltage of a main capacitor across the flashing discharge tube prior to the flashing in order to facilitate the light emission.